The present invention relates to a fuel supply system. For some time, vehicles having hydrogen-operated internal combustion engines have been researched. There are two opposing approaches in regard to the storage of the hydrogen required for operating the internal combustion engine, namely storing gaseous hydrogen at ambient temperature and very high pressure, and storing liquid, cryogenic hydrogen at a temperature of approximately −250° C. and relatively low pressure. The storage of cryogenic hydrogen has the advantage that a higher energy density is achieved than in the storage of gaseous hydrogen. In order to keep the hydrogen liquid for a long time, i.e., multiple weeks, the hydrogen tank must be insulated extremely well. Nonetheless, a certain heat input into the hydrogen tank and thus a continuous vaporization of small quantities of liquid hydrogen are unavoidable. In order to limit the pressure increase in the hydrogen tank, a small quantity of vaporized hydrogen must be discharged to the surroundings during longer shutdown times of the vehicle. The hydrogen to be discharged may be oxidized to form water, i.e., brought into a harmless state.
For the operation of the internal combustion engine, the liquid, cryogenic hydrogen must be preheated from approximately −250° C. to a temperature which is above the ambient temperature. This is already necessary because seals of the fuel system would become brittle and leaky at temperatures that low, which would result in malfunctions at various components of the fuel system, e.g., valves.
If the hydrogen was not preheated as it flowed out of the hydrogen tank, very low temperatures would also occur on the surfaces of the individual fuel system components, i.e., on the surfaces of the fuel lines, on the valves, etc. This would in turn result in the moisture contained in the ambient air condensing locally. The condensed water would freeze immediately on the component surfaces, which would gradually result in complete icing of the fuel system. Because of the extremely low temperature of the hydrogen, the danger would even exist that the ambient air would be liquefied locally in the area of these extremely cold components and/or that oxygen would be distilled out of the ambient air. All of these effects are undesirable and involve significant hazards.
Preheating the hydrogen provided for the combustion in a heat exchanger to a temperature which lies above the ambient temperature is already known from the prior art, the heating power required for the preheating, which is in a range between 20 and 25 kW in experimental engines, being withdrawn from the coolant loop of the internal combustion engine. The heat dissipated unused to the surroundings in typical internal combustion engines via the radiator is thus used for preheating the hydrogen.
The object of the present invention is to provide a fuel supply system for either an internal combustion engine operable using hydrogen or for a fuel cell, in which the hydrogen taken from the hydrogen tank is preheated, it being ensured that the temperatures on surfaces of the individual components of the fuel system are at least equal to the temperature of the ambient air.
The present invention is directed to a fuel supply system for an internal combustion engine operable using hydrogen or for a fuel cell, a hydrogen tank and a heat exchanger being provided. Deep-cooled liquid hydrogen is stored in the hydrogen tank. The stored hydrogen has a temperature which is in the range of approximately −250° C. The heat exchanger is provided for heating the hydrogen taken from the hydrogen tank. The hydrogen is preheated by the heat exchanger from the temperature existing in the hydrogen tank to a temperature which is equal to the ambient temperature or above the ambient temperature. The heat exchanger has a fuel intake, which is connected to the hydrogen tank. From the fuel intake, the hydrogen flows through the hydrogen area of the heat exchanger to a fuel outlet, via which the preheated hydrogen is discharged from the heat exchanger. The heat exchanger also has a coolant intake, via which hot coolant flows from the coolant loop of the internal combustion engine and/or the fuel cell into a coolant area, which is thermally connected to the hydrogen area. In the heat exchanger, the hot coolant delivers heat to the hydrogen and subsequently flows back out of the heat exchanger via a coolant outlet.
The core of the present invention is that the heat exchanger is enclosed by a fluid-tight mantle and/or a fluid-tight envelope. The mantle or envelope may have the form of a box. The mantle may also have the form of a tube, a circular cylinder, or a tank having convex front faces, as is known from tanker vehicles. An intermediate space is provided between the mantle and the heat exchanger, which has a fluid flowing through it. The temperature and the volume flow of the fluid flowing through the intermediate space are tailored in such a way that it is ensured that the temperature on the surface of the mantle is at least equal to the ambient temperature or lies above it. It is thus ensured that neither the ambient air nor the moisture contained therein condenses in the area of the heat exchanger, i.e., on the surface of the mantle. Therefore, icing of the heat exchanger and/or the mantle enclosing the heat exchanger and the downstream components of the fuel system are avoided. In particular, the ambient air is prevented from liquefying locally in the area of the heat exchanger, i.e., oxygen is prevented from distilling out of the ambient air. The components of the fuel system situated after the heat exchanger also are at least at ambient air temperature, because the hydrogen already preheated in the heat exchanger flows through them.
The mantle which encloses the heat exchanger may be flanged directly onto the hydrogen tank. It is thus ensured that all components of the fuel system in which cryogenic hydrogen is located have at least ambient air temperature on their surface.
The mantle which encloses the heat exchanger is preferably impermeable to hydrogen. Therefore, even in the event of a leak in the hydrogen area of the heat exchanger and/or at one of the components of the fuel system inside the mantle which hydrogen flows through, hydrogen may not escape uncontrolled into the ambient air. In addition, a hydrogen sensor may be situated in the intermediate space between the mantle and the heat exchanger and/or in the fluid loop which supplies the intermediate space with fluid, which detects an exit of hydrogen from the heat exchanger into the intermediate space and thus into the fluid loop in case of a leak in one of the hydrogen-conducting components of the fuel system.
The heat exchanger may be connected to the hydrogen tank via multiple lines which hydrogen flows through. Preferably, the heat exchanger is connected via a central coupling to the hydrogen tank. The term central coupling is to be understood to mean that a detachable line coupling is situated in each of the individual connection lines between the hydrogen tank and the heat exchanger. The hydrogen tank and the heat exchanger are therefore detachably connected to one another. This is not only advantageous in regard to mounting and/or dismounting, but rather allows the hydrogen tank and the heat exchanger to be manufactured, tested, and/or optimized independently of one another.
Valves and diverse sensors may be situated shielded in a secondary system capsule in the area between the hydrogen tank and the heat exchanger. The secondary system capsule preferably has hot coolant flowing against it and/or through it. It may thus be ensured that the valves and sensors situated in the secondary system capsule are kept at a certain minimum operating temperature, which is important for perfect functioning of these components. If the valves were not heated, their seals would become brittle, which could result in leaks.
The intermediate space between the mantle and the heat exchanger may be connected to the coolant loop of the internal combustion engine. For the application of a fuel cell, the intermediate space may be connected to the coolant loop of the fuel cell. The intermediate space may be directly connected to the coolant area of the heat exchanger. As an alternative, the intermediate space may also be connected to a separate coolant loop, which is separated from the coolant loop of the internal combustion engine and/or the fuel cell. The intermediate space therefore does not necessarily have to have coolant of the coolant loop of the internal combustion engine and/or the fuel cell flowing through it, but rather may also have another suitable medium flowing through it.
The mantle may be implemented very rigidly as a protective mantle, which protects the heat exchanger and the line system situated inside the mantle from mechanical damage in the event of an accident.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing. The single FIGURE shows the basic principle of the present invention in a schematic illustration.